Need some help diagnosing an electrical problem. To begin it's a 1969 Mach 1, 351 4V with factory tach and running Pertronix III and Pertronix Ignitor coil. Last weekend it cranked up fine and ran briefly, then died. After that when turning the motor over it would catch and fire once, then die. I'm getting the Alternator light in the dash, but tachometer isn't moving. Carburetor, fuel pump, battery, starter, and solenoid all checked out ok. I swapped back to Ford coil and points and no fix to problem. I pulled the plug from back of ignition switch and found what appeared to be a short where the black w/green and dark pink connect at the plug. Installed a replacement pigtail and no fix. I'd like to fix this myself and not have to drag her to a repair shop.
Should I be suspecting a fault in the tach, or start tracking down a short or burned fusible link somewhere in the harness?